Purification of tetra ethyl lead



Patented Sept. 2, 1947 NITED STATES PURIFICATION OF TETRA ETHYL LEAD No Drawing. Application June 2'7, 19%, Serial No. 679,869

8 Claims.

This invention relates to the "purification of tetra ethyl lead and more particularly to the process of removing sludge-forming impurities from the tetra ethyl lead,

In the commercial process or manufacturing tetra ethyl lead and other tetra alkyl lead compounds, lead is reacted with sodium to form a lead. monosodium alloy. This alloy is then reacted With ethyl chloride or with a mixture of ethyl chloride and methyl chloride. After the reaction is complete the tetra ethyl lead and other tetra alkyl lead compounds are removed from the reaction mass by steam distillation. Small quantitles of .finely divided metallic lead and inorganic solids, are carried over with the tetra alkyl lead in the steam distillation. Such solid suspended materials may be removed by the method disclosed in my prior Patent No. 1,975,171.

The lead, employed in such process, usually containssmall amounts of bismuth and other metallic impurities. Such impurities, especially the bismuth,.also react with the ethyl chloride to form organo-metallic compounds which are carried over with the tetra alkyl lead in the steam distillation. These other organo-metallic compounds are less stable than the tetra ethyl lead and tend to decompose and form sludge which settles in the bottom of tank cars, drums, tanks and the like. This sludge will contain up to about 76% bismuth compounds, up to about 20% lead compounds and small amounts of compounds-of other metals. The amount of sludge, obtainable from all of the sludge-forming impurities present in any sample of tetra alkyl lead, is termed the potential sludge content of such sample.

This sludge is objectionable. Frequently, the sludge is highly inflammable and very reactive-on exposure to air. It contains substantial amounts of adsorbed tetra alkyl lead which is always poisonous and hazardous to handle. The sludge, when deposited in tank cars, drums, tanks, -etc., must be periodically removed. The removal and disposal of such sludge is a hazardous task and requires the use of specially designed equipment and specially trained workers.

The formation of sludge and its removal from tank cars, etc. has long been a problem. It has been proposed to incorporate, in tetra ethyl lead, compounds for inhibiting the formation of sludge. These sludge inhibitors have not proved to be entirely satisfactory and have not solved th problem. Previously proposed methods of purifying the crude tetra ethyl'lead have also failed to solve this problem.

In Patent No.' 2,400,'383 granted May 14, 1946,

2 and filed May 15, 1941, jointly by William de Benneville Bertolette and myself, it is disclosed that these problems may be very satisfactorily solved by aerating the tetra ethyl lead, whereby the sludge-forming impurities are caused to form sludge in a small space of time. Such sludge is removed from tetra ethyl lead whereupon the tetra ethyl lead is purified by the substantially complete removal of the sludge-forming impurities. While such process is highly successful, it is sometimes desirable to employ other means to remove the sludge-iorming materials because of the volatility of the tetra alkyl lead compounds.

It is an object of my invention to overcome the problem of sludge formation in tetra ethyl lead and mixtures containing it. Another object is to provide a method for producing stable tetra ethyl lead compositions. A further object is to provide an improved method of purifying tetra ethyl lead. A still further object is to provide a simple and improved method for removing sludge-forming compounds from crude tetra ethyl lead. Other objects are to provide more stable tetra ethyl lead compositions and to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accomplished in accordance with .my invention by Washing crude tetra ethyl lead, containing sludgeforming impurities, with a weak aqueous solution of certain oxidizing agents which will react with the sludge-forming impurities Without causing substantial decomposition of the tetra ethyl lead. I have found that some oxidizing agents, when employed in suitable concentration, will react with the sludge-forming impurities to convert them to insoluble materials or to water-soluble materials or both, without causing substantial decomposition of the tetra ethyl lead. Ihave found further that, by washing crud-e tetra ethyl lead with such weak aqueous solutions of such oxidizing agents, it is possible to remove the sludgeforming impurities substantially completely from crude tetra ethyl lead. The tetra ethyl lead, so treated, is substantially purer and is very much more stable in storage.

Oxidizing agents, which I have found to be effective for my purpose, are the alkali metal chlorites and the alkaline earth 'met'al chlorites in aqueous solution containing a small amount of a non-oxidizing mineral acid such as sulfuric acid and hydrochloric acid.

Generally, the washing of the tetra ethyl lead, in accordance with my invention, is carried out in the presence of air without-any attempt being made to exclude air from the washing equipment,

are substantially ineffective when oxygen, as in the air, is excluded from the equipment and from the washing solution. However, the oxidizing agents of this invention are efiective to remove the sludge-forming impurities, particularly bismuth compounds even when air or other oxygen containing gas was excluded, by replacing the air with nitrogen. 7

While all of the oxidizing agents within my invention appear to operate successfully when they are employed in 1% concentration in water, my invention is not to be limited to the use of 1% concentration. Each of the oxidizing agents may be employed in higher or lower concentration, the exact limits of which will vary with the individual oxidizing agent.

The amount of the aqueous solution to be employed for washing the tetra ethyl lead may be widely varied, it being essential only to employ suflficiently large amounts to provide sufficient oxidizing agent to react with the sludgeforming impurities, particularly the sludge-forming bismuth compounds, present in the tetra ethyl lead. Generally, about one volume of the solution of the oxidizing agent will be suflicient for washing volumes of tetra ethyl lead and re moving the sludge-forming impurities therefrom. In other words, at least [5 volume of the washing solution should be used for each volume of the tetra ethyl lead. In practice, I have found that the best results are obtained by employing approximately one volume of the aqueous solution of the oxidizing agent for each volume of the tetra. ethyl lead. Much larger volumes of the washing solution. can be employed, but without advantage. Attack of the tetra ethyl lead and of the sludge-forming impurities by the oxidizing agent depends upon the particular oxidizing agent employed and its concentration in the aqueous solution, rather than the amount of aqueous solution employed.

In carrying out the washing of the crude tetra ethyl lead in accordance with my invention, the tetra ethyl lead and the aqueous solution. are placed in a suitable container provided with means for agitation. The tetra ethyl lead and the aqueous solution'are agitated and mixed together for a period of time, depending upon the effectiveness of the agitation and the activity of the oxidizing agent, sufficient for the oxidizing agent to react with the sludge-forming impurities. In laboratory size experiments, where the materials may be intimately mixed by shaking,

only a minute or two is required. In large scale operations, where contact between the two materials is less easily accomplished, one to two hours agitation may be necessary. When the reaction of the oxidizing agent with thesludgeforming materials is complete, the agitation is stopped and the mixture allowed to settle where upon 2 layers are formed, the lower layer being the purified tetra ethyl lead and the upper layer being the aqueous solution. When the s1udgeforming impurities are converted to insoluble materiala the will collect in the aqueous layer mainly at the interface between the two layers. The purified tetra ethyl lead may be drawn off from beneath the Water layer. While it is not always necessary to filter the purified tetra ethyl lead, it is generally desirable to filter it so as to insure that no precipitated material will be included in the purified tetra ethyl lead.

In order to illustrate my invention and a mode of carrying the same into effect, the following example is given:

Example A batch of tetra ethyl lead with a potential sludge content of 0.110 mg. per ml. was placed in a suitable tank provided with an agitator and necessary connection for adding Water and other materials and for introducing and remov-' ing tetra ethyl lead. An equal volume of water,

containing 1% of sodium chlorite and 1% of sulfuric acid, was added and the contents agitated for a short time. The mixture was allowed to settle and the tetra ethyl lead was drawn off from beneath the aqueous layer. The purified tetra ethyl lead had a potential sludge content of 0.0025 mg. per 100 ml.

V It will be understood that the preceding example and the oxidizing agents specifically named are given for illustrative purposesand that various modifications and variations may be made therein without departing from the spirit or scope of my invention. While I have disclosed the mixing of the tetra ethyl lead with the desired volume of the aqueous solution in a single operation, and .that is the preferred method of practicing my invention, it will be apparent that the tetra ethyl lead can be subjected to successive washings with smaller increments of the washing solution. Also, the washing solution may contain trisodium phosphate or other wetting agent disclosed in my Patent No. 1,975,171 so as to at the sametime remove finely divided metallic lead with my invention may also be employed in combination with the aeration process disclosed in Patent No. 2,400,383, before referred to. In such case, the oxidizing agents willassist in the oxidation of the sludge-forming impurities by the air even when the oxidizing agents are employed in very low concentrations at which they themselves are ineifective to remove the sludge-forming impurities. Under such conditions, the oxidizing agents appear to act as catalysts in the aeration process.

This application is in part a continuation of my copending application Serial No. 489,067, filed May 27, 1943, for Purification of tetra ethyl lead, now Patent 2,410,356.

I claim:

1. The method of purifying steam distilledtetra ethyl lead containing sludge-formin impurities, which comprises agitating the tetra ethyl lead with at least volume of a weak aqueous solution. of an oxidizing agent of the'class consisting of alkali metal chlorites and alkaline earth metal chlorites, which solution contains about 1% of a non-oxidizing mineral acid, for sufiicient time for the oxidizing agent to react with the sludge-forming impurities, the concentrationof the oxidizing agent in the aqueous solution being sufficient to react with the sludge-formin impurities, but insufficient to cause substantial decomposition of the tetra ethyl lead, settling .the mixture and separating the'tetra ethyl lead from the aqueous solution and the reaction products of the oxidizing. agent with the sludge-forming impurities. I

2. The method of purifying steam'distilled tetra ethyl lead containin sludge-formin impurities, which comprises agitating the tetra ethyl lead with approximately 1 volume of a Weak aqueous solution of an oxidizing agent of the class consisting of alkali metal chlorites and alkaline earth metal chlorites, which solution contains about 1% of a non-oxidizing mineral acid, for sufficient time for the oxidizing agent to react with the slud forming impurities, the concentration of the oxidizing agent in the aqueous solution being sufiicient to react with the sludge-forming impurities but insufiicient to cause substantial decomposition of the tetra ethyl lead, settling the mixture and separating the tetraethyl lead from the aqueous solution and the reaction products of the oxidizing agent with the sludge-forming impurities.

3. The method of purifying steam distilled tetra ethyl lead containing sludge-forming impurities, which comprises agitating the tetra ethyl lead with at least /5 volume of a weak aqueous solution of an oxidizing agent of the class consisting of alkali metal chlorites and alkaline earth metal chlorites, which solution contains about 1% of a non-oxidizing mineral acid, for sufilcient time for the oxidizing agent to react with the sludge-forming impurities, the concentration of the oxidizing agent in the aqueous solution being approximately settling the mixture and separating the tetra ethyl lead from the aqueous solution and the reaction products of the oxidizing agent with the sludge-forming impurities.

4. The method of purifying steam distilled tetra ethyl lead containing sludge-forming impurities, which comprises agitating the tetra ethyl lead with at least volume of a weak aqueous solution of sodium chlorite containing about 1% of a nonoxidizing mineral acid, for suflicient time for the sodium chlorite to react with the sludge-forming impurities, the concentration of the sodium chlo rite in the aqueous solution being sufiicient to react with the sludge-forming impurities, but insufiicient to cause substantial decomposition of the tetra ethyl lead, settling the mixture and separating the tetra ethyl lead from the aqueous solution and the reaction products of the sodium chlorite with the sludge-forming impurities.

5. The method of purifying steam distilled tetra ethyl lead containing sludge-forming impurities, which comprises agitatin the tetra ethyl lead with approximately 1 volume of a Weak aqueous solution of sodium chlorite containing about 1% of a nonoxidizing mineral acid, for sufficient time for the sodium chlorite to react with the sludgeforming impurities, the concentration of the sodium chlorite in the aqueous solution being suflicient to react with the sludge-forming impurities but insuflicient to cause substantial decomposition of the tetra ethyl lead, settling the mixture and separating the tetraethyl lead from the aqueous solution and the reaction products of the sodium chlorite with the sludge-forming impurities.

6. The method of purifying steam distilled tetra ethyl lead containing sludge-formin impurities, which comprises agitating the tetra ethyl lead "with at least /5 volume of a weak aqueous solution of sodium chlorite containing about 1% of a non-oxidizing mineral acid, for sufiicient time for the sodium chlorite to react with the sludgeforming impurities, the concentration of the sodium chlorite in the aqueous solution being approximately 1%, settling the mixture and separating the tetra ethyl lead from the aqueous solution and the reaction products of the sodium chlorite with the sludge-forming impurities,

7. The method of purifying steam distilled tetra ethyl lead containing sludge-formin impurities, which comprises agitating the tetra ethyl lead with at least /5 volume of a weak aqueous solution of sodium chlorite containing about 1% of sulfuric acid for suflicient time for the sodium chlorite to react with the sludge-forming impurities, the concentration of the sodium chlorite in the aqueous solution being sufiicient to react with the sludge-formin impurities, but insufiicient to cause substantial decomposition of the tetra ethyl lead, settling the mixture and separating the tetra ethyl lead from the aqueous solution and the reaction products of the sodium chlorite with the sludge-forming impurities.

8. The method of purifying steam distilled tetra ethyl lead containing sludge-forming impurities, which comprises agitating the tetra ethyl lead with approximately 1 volume of a weak aqueous solution of sodium chlorite containing about 1% of sulfuric acid, for sufficient time for the sodium chlorite to react with the sludge-forming impurities, the concentration of the sodium chlorite in the aqueous solution being approximately 1%, settling the mixture and separating the tetra ethyl lead from the aqueous solution and the reaction products of the sodium chlorite with the sludgeforming impurities.

ALFRED E. PARMELEE. 

